The movie opened in 1935 and appears to be set in the 1930s. The original Arthur Conan Doyle serial, from which the screenplay was written, was published in 1914-15, and was set in the 1880s.
The movie's flashback to the U.S.A. introduces the Scowlers, a secret society of thugs. The fictional Scowlers appears to be based on the Molly Maguires, an actual secret society of immigrant Irish coal miners in eastern Pennsylvania, USA, in the 1860s and 1870s. They were set up as a secret network of local committees, and they did not brand their members, since they wished to remain anonymous.
Conditions in the mines were abominable, as this was long before child labor laws, a minimum wage, suitable standards on working conditions, or any organized form of labor union. The Mollies fought back with threats, beatings, riots, and murder against abusive mine owners, supervisors, police, and anyone who spoke out against them.
The powerful owner of many coal mines hired the Pinkerton Detective Agency to infiltrate the society, and one of their detectives managed to join the Mollies and stay under cover for nearly five years. When his investigation was finished, trials in were held, twenty convicted society members were hanged, and the Mollie Maguires were history.
So the film's use of a local committee of thugs, and the triumph of the Pinkerton Detective Agency, are quite realistic, based on Pennsylvania history.